In vivo drug delivery is now accomplished by a number of technologies including actuator pumps, osmotic pumps, and release from highly-engineered materials. Implantable controlled release devices for drug delivery have been developed. Certain devices rely upon the gradual release of a drug from a polymeric carrier over time, due to degradation of the carrier. Polymer-based drug release devices are being developed that include a drug in a ferropolymer that may be manipulated by an externally applied magnetic field, thus influencing the drug release. MEMS-based drug release devices that include integrated electrical circuitry are also under development, as are MEMS-based systems for performing chemical reactions. Implantable osmotic pump devices have been developed for drug delivery purposes.